Calculate the number of years to reduce pollution in Lake Erie to each level.

a. 40%

b. 30%

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The following figures, representing years, were found in this way. Fortunately, the pollution in Lake Superior is quite low at present. As mentioned before, assumptions 3, 4, and 5 are questionable. For persistent pollutants like DDT, the estimated cleanup times may be too low. For other pollutants, how assumptions 4 and 5 affect cleanup times is unclear. However, the values of 1/k given in the figure probably provide rough lower bounds for the cleanup times of persistent pollutants. Lake Erie 50% 2 Michigan 21 Superior 131 20% 4 50 304 10% 6 71 435 5% 8 92 566